1. Field of the Invention
The present invention relates to pendulum arrangements of pendulum clocks and more particularly to a pendulum arrangement of a pendulum clock in which a magnetic urging device swings a pendulum by means of an electromagnet and a permanent magnet.
2. Description of the Prior Art
The pendulum clock is historically old and various types of pendulum clocks have been produced in such that the standard rotation for the clock operation is obtained on the basis of accurate swinging movement of pendulum. The pendulum clock in the prior art provides standard oscillation for clock operation based on the combination of a pendulum and an escapement consisted of a pallet fork and an escape wheel, but such combination of the pendulum and the escapement is recently used for a pure decoration as various types of accurate oscillating sources have been being developed. For the moving source of pendulum swing, practically used are both types of the escapement consisted of a pallet fork and an escape wheel and the magnetic urging device.
The mechanism described in the following is used as the magnetic as the magnetic urging device in the pendulum arrangements of the pendulum clocks in the prior art.
FIG. 1 is an illustration of the rear elevation of a pendulum clock which is composed of a pendulum as a pure ornamental means. A clock movement 12, a supporting shaft 14 and a pendulum driving curcuit board 16 are respectively fixed on a base plate 10 which is installed on the housing, not illustrated. The supporting shaft 14 is formed in square and arranged on the base plate 10 in such a way that an edge 14a is positioned at the upper end. Around the supporting shaft 14 freely arranged is a supporting pipe 18 which is cylindrically formed with larger diameter than the supporting shaft 14.
One end of a pendulum arm 20 is attached to the supporting pipe 18 mentioned above and a pendulum disc 22 is detachably hung on the other end of the pendulum arm 20. The edge 14a of the supporting shaft 14 acts as the fulcrum of the swinging movement of the pendulum arm 20.
In order to swing the pendulum arm 20 an electromagnet 28 including a moving coil and a steel core 26 is arranged on the pendulum driving circuit board 16, and a permanent magnet 30 is solidly attached to the pendulum arm 20 with slight air gap against the electromagnet so that the cooperative operations of the electromagnet 28 and the permanent magnet 30 can swing the pendulum arm 20.
The pendulum arrangement of the pendulum clock in the prior art is as mentioned above and supply of electric current to the moving coil 24 of the electromagnet 28 at an adequet time interval makes the permanent magnet 30 to repeat atraction and repulsion to and against the steel core 26 so that the pendulum arm 20 performs a requested swinging action as shown in FIG. 2.
Furthermore, the pendulum arrangement using the magnetic urging device of the electromagnet 28 and the permanent magnet 30 can be obtianed as a unit, and has various types of effects as well as cannot put no load on the time indicating wheel train and can use a pendulum with the large force of inertia.
In the pendulum arrangement of the pendulum clock of this kind, however, in case the clock body is tilted at .DELTA..theta. from its vertical position as shown in FIG. 3, there is such drawbacks that the permanent magnet 30 does not face to the electromagnet in right way since the electromagnet 28 is fixed to the clock body.
In other words, the installed position of the electromagnet 28 moves from the vertical line at .DELTA..theta., but the pendulum arm 20 always swings to the left and the right from its vertical position at .theta. regardless of the tilt of the clock body. Accordingly, since the swinging angle of the pendulum arm 20 to the left in FIG. 3 shows .theta.+.DELTA..theta. and the swinging angle to the right shows .theta.-.DELTA..theta., magnetic urging cannot be provided with stability.